There are various designs of hand dryer on the market, which are typically installed in public washrooms as an alternative to paper towels.
Hand dryers rely on airflow to dry a user's hands. The airflow is typically discharged through one or more air outlets on the hand dryer and the user holds the hands in close proximity to the air outlet(s) so that the airflow is directed onto the user's hands to provide a drying effect.
The principal drying mechanism may differ between different types of hand dryer. The drying mechanism may be evaporative, in which case the airflow will tend to be heated. Alternatively, the drying mechanism may rely mainly on a momentum-drying effect at the surface of the hands, in which case the airflow will tend to be discharged at high velocity (in excess of 80 m/s, and typically in excess of 140 m/s).
In each case, the airflow is often generated using a motor-driven fan unit which is located inside the hand dryer. Air is drawn into the fan unit through an air intake on the external casing of the hand dryer. The air is often filtered upstream of the fan unit using an air-filter so that the air discharged through the air outlet is filtered air. This makes the hand dryer more hygienic for users.